Organopolysiloxane compositions which can be crosslinked with an organic peroxide compound and which contain barium peroxide, barium oxide or magnesium oxide are described in U.S. Pat. Nos. 3,261,801 to Wormuth, 3,468,838 to Loraine et al and 3,865,778 to Christie. Also U.S. Pat. No. 3,004,859 to Lichtewallner, German Pat. No. 1,141,082 to Dow Corning Corporation and British Pat. No. 1,132,853 to Midland Silicones Limited describe diorganopolysiloxane-based compositions which can be crosslinked with an organic peroxide, containing at least one inorganic solid which can be treated with an organosilicon compound to render the same hydrophobic. However, none of the organopolysiloxane compositions known heretofore which can be crosslinked with organic peroxide compounds contain calcium hydroxide which has been treated with an organosilicon compound to render the same hydrophobic to form elastomers which after heating in the presence of air have a low compression set, have increased resistance to reversion in a sealed system and exhibit increased stability to hot fluid hydrocarbons, or partially oxidized hot fluid hydrocarbons or not motor oils.
Therefore, it is an object of this invention to provide organopolysiloxane compositions which are crosslinked with organic peroxide compounds to form elastomers. Another object of this invention is to provide crosslinkable organopolysiloxane compositions which contain a basic solid that is treated with a compound capable of imparting hydrophobic properties to the basic solid. Still another object of this invention is to provide an organopolysiloxane elastomer having improved compression set. A further object of this invention is to provide organopolysiloxane elastomers having increased resistance to reversion in a sealed system. A still further object of this invention is to provide organopolysiloxane compositions, which are crosslinked with an organic peroxide compound, containing calcium hydroxide which has been treated with an organosilicon compound to render the calcium hydroxide hydrophobic.